Analog to digital converters (ADC), as their name implies, generate multi-bit digital values from analog signals. ADCs are used throughout modern electronic systems, often to convert the outputs of sensors and transducers to digital form for further processing by computer systems.
There are several types of ADCs. One known architecture, called the successive approximation register analog-to-digital converter (SAR ADC) samples an input voltage and compares it to a plurality of threshold voltages on a bit by bit basis. When converting an analog voltage to a 14-bit digital codeword, an SAR ADC will perform 14 decisions, one decision for each bit in the codeword. To this end, the SAR ADC often includes one or more capacitor arrays to store sampled voltages and to generate reference voltages and a comparator to compare the sampled voltage to each reference voltage and perform bit decisions.
In traditional, high-resolution SAR ADCs, it is often the performance of the comparator that limits the maximum conversion rate of the ADC. The performance of the comparator is usually defined by a worst case resolution time, representing a time required to resolve a minimum differential voltage at the comparator's inputs. Ordinary SAR ADCs clock their comparators at a constant clock rate commensurate with this worst-case performance. However, by definition, this minimum error only occurs during one bit-trial of a multi-bit conversion process. During all other bit trials, the errors at the comparator inputs are larger, so the comparator often settles at a decision faster than the worst-case performance. Since ordinary SAR ADCs clock their comparators at a constant clock rate representing the worst-case settling characteristics, the SAR ADCs operate inefficiently.
Accordingly, the inventors perceive a need in the art for an ADC that provides increased processing capability as compared to ADCs clocked under the worst case scenario. The inventors perceive a need in the art for an ADC that performs bit decisions as fast as the ADC's comparator is capable of making them.